August 26, 2016

This image shows the galaxy Messier 94, which lies in the small northern constellation of the Hunting Dogs, about 16 million light-years away.

Within the bright ring around Messier 94 new stars are forming at a high rate and many young, bright stars are present within it – thanks to this, this feature is called a starburst ring.

The cause of this peculiarly shaped star-forming region is likely a pressure wave going outwards from the galactic centre, compressing the gas and dust in the outer region. The compression of material means the gas starts to collapse into denser clouds. Inside these dense clouds, gravity pulls the gas and dust together until temperature and pressure are high enough for stars to be born.

This colourful view shows the star-forming region LHA 120-N44 in the Large Magellanic Cloud, a small satellite galaxy of the Milky Way. This picture combines the view in visible light from the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile with images in infrared light and X-rays from orbiting satellite observatories.

At the centre of this very rich region of gas, dust and young stars lies the star cluster NGC 1929. Its massive stars produce intense radiation, expel matter at high speeds as stellar winds, and race through their short but brilliant lives to explode as supernovae. The winds and supernova shock waves have carved out a huge cavity, called a superbubble, in the surrounding gas.

Observations with NASA's Chandra X-ray Observatory (shown here in blue) reveal hot regions created by these winds and shocks, while infrared data from NASA's Spitzer Space Telescope (shown in red) outline where the dust and cooler gas are found. The visible-light view from the MPG/ESO 2.2-metre telescope (in yellow) completes the picture and shows the hot young stars themselves as well as the glowing clouds of gas and dust that surround them.

Combining these different views of this dramatic region has allowed astronomers to solve a mystery: why are N44, and similar superbubbles, giving off such strong X-rays? The answer seems to be that there are two extra sources of bright X-ray emission: supernova shock waves striking the walls of the cavities, and hot material evaporating from the cavity walls. This X-ray emission from the edge of the superbubble shows up clearly in the picture.

Home to some of the largest stars ever discovered, the open stellar cluster Pismis 24 blazes from the core of NGC 6357, a nebula in the constellation of Scorpius (the Scorpion). Several stars in the clusters weigh in at over 100 times the mass of the Sun, making them real monster stars. The strange shapes taken by the clouds are a result of the huge amount of blazing radiation emitted by these massive, hot stars. The gas and dust of the nebula hide huge baby stars in the nebula from telescopes observing in visible light, as well as adding to the hazy appearance of the image.

This image combines observations performed through three different filters in visible light (B, V, R) with the 1.5-metre Danish telescope at the ESO La Silla Observatory in Chile.

August 25, 2016

Our magnificent Milky Way galaxy is radiant over La Silla Observatory. The ESO 3.6-metre telescope is shown to the right, now home to the world's foremost extrasolar planet hunter: High Accuracy Radial velocity Planet Searcher (HARPS), a spectrograph with unrivalled precision.

This image of the sky around the bright star Alpha Centauri AB also shows the much fainter red dwarf star, Proxima Centauri, the closest star to the Solar System. The picture was created from pictures forming part of the Digitized Sky Survey 2. The blue halo around Alpha Centauri AB is an artifact of the photographic process, the star is really pale yellow in colour like the Sun.

Proxima Centauri appears as a faint red star towards the lower-right of the picture.

This wide-field image shows the Milky Way stretching across the southern sky. The beautiful Carina Nebula (NGC 3372) is seen at the right of the image glowing in red. It is within this spiral arm of our Milky Way that the bright star cluster NGC 3603 resides. At the centre of the image is the constellation of Crux (The Southern Cross). The bright yellow/white star at the left of the image is Alpha Centauri, in fact a system of three stars, at a distance of about 4.4 light-years from Earth. The star Alpha Centauri C, Proxima Centauri, is the closest star to the Solar System.

This artist’s impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also appears in the image between the planet and Proxima itself. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface.

August 24, 2016

This artist’s impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also appears in the image to the upper-right of Proxima itself. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface.

Astronomers using ESO telescopes and other facilities have found clear evidence of a planet orbiting the closest star to Earth, Proxima Centauri. The long-sought world, designated Proxima b, orbits its cool red parent star every 11 days and has a temperature suitable for liquid water to exist on its surface. This rocky world is a little more massive than the Earth and is the closest exoplanet to us — and it may also be the closest possible abode for life outside the Solar System.

Just over four light-years from the Solar System lies a red dwarf star that has been named Proxima Centauri as it is the closest star to Earth apart from the Sun. This cool star in the constellation of Centaurus is too faint to be seen with the unaided eye and lies near to the much brighter pair of stars known as Alpha Centauri AB.

During the first half of 2016 Proxima Centauri was regularly observed with the HARPS spectrograph on the ESO 3.6-metre telescope at La Silla in Chile and simultaneously monitored by other telescopes around the world. This was the Pale Red Dot campaign, in which a team of astronomers led by Guillem Anglada-Escudé, from Queen Mary University of London, was looking for the tiny back and forth wobble of the star that would be caused by the gravitational pull of a possible orbiting planet.

As this was a topic with very wide public interest, the progress of the campaign between mid-January and April 2016 was shared publicly as it happened on the Pale Red Dot website and via social media. The reports were accompanied by numerous outreach articles written by specialists around the world.

Guillem Anglada-Escudé explains the background to this unique search: “The first hints of a possible planet were spotted back in 2013, but the detection was not convincing. Since then we have worked hard to get further observations off the ground with help from ESO and others. The recent Pale Red Dot campaign has been about two years in the planning.”

The Pale Red Dot data, when combined with earlier observations made at ESO observatories and elsewhere, revealed the clear signal of a truly exciting result. At times Proxima Centauri is approaching Earth at about 5 kilometres per hour — normal human walking pace — and at times receding at the same speed. This regular pattern of changing radial velocities repeats with a period of 11.2 days. Careful analysis of the resulting tiny Doppler shifts showed that they indicated the presence of a planet with a mass at least 1.3 times that of the Earth, orbiting about 7 million kilometres from Proxima Centauri — only 5% of the Earth-Sun distance.

Guillem Anglada-Escudé comments on the excitement of the last few months: "I kept checking the consistency of the signal every single day during the 60 nights of the Pale Red Dot campaign. The first 10 were promising, the first 20 were consistent with expectations, and at 30 days the result was pretty much definitive, so we started drafting the paper!"

Red dwarfs like Proxima Centauri are active stars and can vary in ways that would mimic the presence of a planet. To exclude this possibility the team also monitored the changing brightness of the star very carefully during the campaign using the ASH2 telescope at the San Pedro de Atacama Celestial Explorations Observatory in Chile and the Las Cumbres Observatory telescope network. Radial velocity data taken when the star was flaring were excluded from the final analysis.

Although Proxima b orbits much closer to its star than Mercury does to the Sun in the Solar System, the star itself is far fainter than the Sun. As a result Proxima b lies well within the habitable zone around the star and has an estimated surface temperature that would allow the presence of liquid water. Despite the temperate orbit of Proxima b, the conditions on the surface may be strongly affected by the ultraviolet and X-ray flares from the star — far more intense than the Earth experiences from the Sun.

Two separate papers discuss the habitability of Proxima b and its climate. They find that the existence of liquid water on the planet today cannot be ruled out and, in such case, it may be present over the surface of the planet only in the sunniest regions, either in an area in the hemisphere of the planet facing the star (synchronous rotation) or in a tropical belt (3:2 resonance rotation). Proxima b's rotation, the strong radiation from its star and the formation history of the planet makes its climate quite different from that of the Earth, and it is unlikely that Proxima b has seasons.

This discovery will be the beginning of extensive further observations, both with current instruments and with the next generation of giant telescopes such as the European Extremely Large Telescope (E-ELT). Proxima b will be a prime target for the hunt for evidence of life elsewhere in the Universe. Indeed, the Alpha Centauri system is also the target of humankind’s first attempt to travel to another star system, the StarShot project.

Guillem Anglada-Escudé concludes: "Many exoplanets have been found and many more will be found, but searching for the closest potential Earth-analogue and succeeding has been the experience of a lifetime for all of us. Many people’s stories and efforts have converged on this discovery. The result is also a tribute to all of them. The search for life on Proxima b comes next..."

August 23, 2016

The massive, young stellar grouping, called R136, is only a few million years old and resides in the 30 Doradus Nebula, a turbulent star-birth region in the Large Magellanic Cloud (LMC), a satellite galaxy of our Milky Way. Many of the stars are among the most massive known. Several of them are over 100 times more massive than our Sun. These hefty stars are destined to become supernovae in a few million years.

The image, taken by Hubble's Wide Field Camera 3, spans about 100 light-years. The nebula is close enough to Earth that Hubble can resolve individual stars, giving astronomers important information about the stars' birth and evolution.

The brilliant stars are carving deep cavities in the surrounding material by unleashing a torrent of ultraviolet light, and hurricane-force stellar winds (streams of charged particles), which are etching away the enveloping hydrogen gas cloud in which the stars were born. The image reveals a fantasy landscape of pillars, ridges, and valleys, as well as a dark region in the center that roughly looks like the outline of a holiday tree. Besides sculpting the gaseous terrain, the brilliant stars can also help create a successive generation of offspring. When the winds hit dense walls of gas, they create shocks, which may be generating a new wave of star birth.

The movement of the LMC around the Milky Way may have triggered the massive cluster's formation in several ways. The gravitational tug of the Milky Way and the companion Small Magellanic Cloud may have compressed gas in the LMC. Also, the pressure resulting from the LMC plowing through the Milky Way's halo may have compressed gas in the satellite. The cluster is a rare, nearby example of the many super star clusters that formed in the distant, early universe, when star birth and galaxy interactions were more frequent. Previous Hubble observations have shown astronomers that super star clusters in faraway galaxies are ubiquitous. The LMC is located 170,000 light-years away and is a member of the Local Group of Galaxies, which also includes the Milky Way.

The Hubble image was taken at infrared wavelengths (1.1 microns and 1.6 microns). Hubble sees through the dusty nebula, revealing many stars that cannot be seen in visible light. The large bright star just above the center of the image is in the 30 Doradus nebula. The Hubble observations of 30 Doradus were made October 20-27, 2009.

NASA's Spitzer and Hubble Space Telescopes teamed up to expose the chaos that baby stars are creating 1,500 light years away in a cosmic cloud called the Orion nebula. This striking composite indicates that four monstrously massive stars, collectively called the "Trapezium," at the center of the cloud may be the main culprits in the Orion constellation, a familiar sight in the fall and winter night sky in the northern hemisphere. Their community can be identified as the yellow smudge near the center of the image.

Swirls of green in Hubble's ultraviolet and visible-light view reveal hydrogen and sulfur gas that have been heated and ionized by intense ultraviolet radiation from the Trapezium's stars. Meanwhile, Spitzer's infrared view exposes carbon-rich molecules called polycyclic aromatic hydrocarbons in the cloud. These organic molecules have been illuminated by the Trapezium's stars, and are shown in the composite as wisps of red and orange. On Earth, polycyclic aromatic hydrocarbons are found on burnt toast and in automobile exhaust.

Stellar winds from clusters of newborn stars scattered throughout the cloud etched all of the well-defined ridges and cavities in Orion. The large cavity near the right of the image was most likely carved by winds from the Trapezium's stars. Located 1,500 light-years away from Earth, the Orion nebula is the brightest spot in the sword of the Orion, or the "Hunter" constellation. The cosmic cloud is also our closest massive star-formation factory, and astronomers believe it contains more than 1,000 young stars.

This image, courtesy of the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS), captures the glow of distant stars within NGC 5264, a dwarf galaxy located just over 15 million light-years away in the constellation of Hydra (The Sea Serpent).

Dwarf galaxies like NGC 5264 typically possess around a billion stars — just one per cent of the number of stars found within the Milky Way. They are usually found orbiting other, larger, galaxies such as our own, and are thought to form from the material left over from the messy formation of their larger cosmic relatives.

NGC 5264 clearly possesses an irregular shape — unlike the more common spiral or elliptical galaxies — with knots of blue star formation. Astronomers believe that this is due to the gravitational interactions between NGC 5264 and other galaxies nearby. These past flirtations sparked the formation of new generations of stars, which now glow in bright shades of blue.

August 22, 2016

A bluish-white spiral galaxy hangs delicately in the cold vacuum of space. Known as NGC 1376, this snowflake-shaped beauty was observed with the Hubble Space Telescope.

Concentrated along the spiral arms of NGC 1376, bright blue knots of glowing gas highlight areas of active star formation. These regions show an excess of light at ultraviolet (UV) wavelengths because they contain brilliant clusters of hot, newborn stars that are emitting UV light. The less intense, red areas near the core and between the arms consist mainly of older stars. The reddish dust lanes delineate cooler, denser regions where interstellar clouds may collapse to form new stars. Visually intermingled between the spiral arms is a sprinkling of reddish background galaxies.

NGC 1376 resides over 180 million light-years away from Earth in the constellation Eridanus. This galaxy belongs to a class of spirals that are seen nearly face on from our line of sight. Its orientation aids astronomers in studying details and features of the galaxy from a relatively unobscured vantage point. One such feature is represented by stars that vary in brightness over time. In 1990, NGC 1376 was home to a supernova explosion (SN 1990go) that rivaled the brightness of the entire nucleus (as seen from ground-based telescopes) for several weeks.

The story of how this galaxy came to be photographed by Hubble is somewhat unique. During the November 2006 observations of a nearby dwarf galaxy with Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) detector, careful planning allowed for NGC 1376 to be visible in the field of view of the Advanced Camera for Surveys (ACS) at the same time. Thus, Hubble was able to get two galaxies for the price of one. Although the use of parallel instruments onboard Hubble is not uncommon, capturing two interesting targets is rather rare.

Initial ground-based observations of NGC 1376 and its nearby dwarf companion implied that the two might be interacting with each other, but the Hubble observations demonstrates no obvious signs of interaction. This is not surprising since the dwarf galaxy would have little effect on this giant spiral galaxy. NGC 1376 was imaged with ACS in eight filters ranging from blue to visible to infrared light. Four of the filtered images that show the most colour separation were used in this Hubble composite of NGC 1376.

A new Chandra image of SN 1006 provides new details about the remains of an exploded star.

This explosion was witnessed from Earth over a millennium ago.

The Chandra data provides the best map to date of the debris field including information on important elements expanding into space.

SN 1006 belongs to a class of supernova used to measure the expansion of the Universe.

When the object we now call SN 1006 first appeared on May 1, 1006 A.D., it was far brighter than Venus and visible during the daytime for weeks. Astronomers in China, Japan, Europe, and the Arab world all documented this spectacular sight. With the advent of the Space Age in the 1960s, scientists were able to launch instruments and detectors above Earth's atmosphere to observe the Universe in wavelengths that are blocked from the ground, including X-rays. SN 1006 was one of the faintest X-ray sources detected by the first generation of X-ray satellites.

A new image of SN 1006 from NASA's Chandra X-ray Observatory reveals this supernova remnant in exquisite detail. By overlapping ten different pointings of Chandra's field-of-view, astronomers have stitched together a cosmic tapestry of the debris field that was created when a white dwarf star exploded, sending its material hurtling into space. In this new Chandra image, low, medium, and higher-energy X-rays are colored red, green, and blue respectively.

The Chandra image provides new insight into the nature of SN1006, which is the remnant of a so-called Type Ia supernova . This class of supernova is caused when a white dwarf pulls too much mass from a companion star and explodes, or when two white dwarfs merge and explode. Understanding Type Ia supernovas is especially important because astronomers use observations of these explosions in distant galaxies as mileposts to mark the expansion of the Universe.

The new SN 1006 image represents the most spatially detailed map yet of the material ejected during a Type Ia supernova. By examining the different elements in the debris field -- such as silicon, oxygen, and magnesium -- the researchers may be able to piece together how the star looked before it exploded and the order that the layers of the star were ejected, and constrain theoretical models for the explosion.

Scientists are also able to study just how fast specific knots of material are moving away from the original explosion. The fastest knots are moving outward at almost eleven million miles per hour, while those in other areas are moving at a more leisurely seven million miles per hour. SN 1006 is located about 7,000 light years from Earth. The new Chandra image of SN 1006 contains over 8 days worth of observing time by the telescope.

The MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile has captured a richly colourful view of the bright star cluster NGC 3532. Some of the stars still shine with a hot bluish colour, but many of the more massive ones have become red giants and glow with a rich orange hue.

NGC 3532 is a bright open cluster located some 1300 light-years away in the constellation of Carina (The Keel of the ship Argo). It is informally known as the Wishing Well Cluster, as it resembles scattered silver coins which have been dropped into a well. It is also referred to as the Football Cluster, although how appropriate this is depends on which side of the Atlantic you live. It acquired the name because of its oval shape, which citizens of rugby-playing nations might see as resembling a rugby ball.

This very bright star cluster is easily seen with the naked eye from the southern hemisphere. It was discovered by French astronomer Nicolas Louis de Lacaille whilst observing from South Africa in 1752 and was catalogued three years later in 1755. It is one of the most spectacular open star clusters in the whole sky.

NGC 3532 covers an area of the sky that is almost twice the size of the full Moon. It was described as a binary-rich cluster by John Herschel who observed “several elegant double stars” here during his stay in southern Africa in the 1830s. Of additional, much more recent, historical relevance, NGC 3532 was the first target to be observed by the NASA/ESA Hubble Space Telescope, on 20 May 1990.

This grouping of stars is about 300 million years old. This makes it middle-aged by open star cluster standards. The cluster stars that started off with moderate masses are still shining brightly with blue-white colours, but the more massive ones have already exhausted their supplies of hydrogen fuel and have become red giant stars. As a result the cluster appears rich in both blue and orange stars. The most massive stars in the original cluster will have already run through their brief but brilliant lives and exploded as supernovae long ago. There are also numerous less conspicuous fainter stars of lower mass that have longer lives and shine with yellow or red hues. NGC 3532 consists of around 400 stars in total.

The background sky here in a rich part of the Milky Way is very crowded with stars. Some glowing red gas is also apparent, as well as subtle lanes of dust that block the view of more distant stars. These are probably not connected to the cluster itself, which is old enough to have cleared away any material in its surroundings long ago.

August 21, 2016

Several thousand years ago, a star some 160 000 light-years away from us exploded, scattering stellar shrapnel across the sky. The aftermath of this energetic detonation is shown here in this striking image from the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3.

The exploding star was a white dwarf located in the Large Magellanic Cloud, one of our nearest neighbouring galaxies. Around 97% of stars within the Milky Way that are between a tenth and eight times the mass of the Sun are expected to end up as white dwarfs. These stars can face a number of different fates, one of which is to explode as supernovae, some of the brightest events ever observed in the Universe. If a white dwarf is part of a binary star system, it can siphon material from a close companion. After gobbling up more than it can handle — and swelling to approximately one and a half times the size of the Sun — the star becomes unstable and ignites as a Type Ia supernova.

This was the case for the supernova remnant pictured here, which is known as DEM L71. It formed when a white dwarf reached the end of its life and ripped itself apart, ejecting a superheated cloud of debris in the process. Slamming into the surrounding interstellar gas, this stellar shrapnel gradually diffused into the separate fiery filaments of material seen scattered across this skyscape.

The small smattering of bright blue stars in the upper left of this vast 615 megapixel ESO image is the perfect cosmic laboratory in which to study the life and death of stars. Known as Messier 18 this star cluster contains stars that formed together from the same massive cloud of gas and dust. This image, which also features red clouds of glowing hydrogen and dark filaments of dust, was captured by the VLT Survey Telescope (VST) located at ESO’s Paranal Observatory in Chile.

Messier 18 was discovered and catalogued in 1764 by Charles Messier — for whom the Messier Objects are named — during his search for comet-like objects. It lies within the Milky Way, approximately 4600 light-years away in the constellation of Sagittarius, and consists of many sibling stars loosely bound together in what is known as an open cluster.

There are over 1000 known open star clusters within the Milky Way, with a wide range of properties, such as size and age, that provide astronomers with clues to how stars form, evolve and die. The main appeal of these clusters is that all of their stars are born together out of the same material.

In Messier 18 the blue and white colours of the stellar population indicate that the cluster’s stars are very young, probably only around 30 million years old. Being siblings means that any differences between the stars will only be due to their masses, and not their distance from Earth or the composition of the material they formed from. This makes clusters very useful in refining theories of star formation and evolution.

Astronomers now know that most stars do form in groups, forged from the same cloud of gas that collapsed in on itself due to the attractive force of gravity. The cloud of leftover gas and dust — or molecular cloud — that envelops the new stars is often blown away by their strong stellar winds, weakening the gravitational shackles that bind them. Over time, loosely bound stellar siblings like those pictured here will often go their separate ways as interactions with other neighbouring stars or massive gas clouds nudge, or pull, the stars apart. Our own star, the Sun, was most likely once part of a cluster very much like Messier 18 until its companions were gradually distributed across the Milky Way.

The dark lanes that snake through this image are murky filaments of cosmic dust, blocking out the light from distant stars. The contrasting faint reddish clouds that seem to weave between the stars are composed of ionised hydrogen gas. The gas glows because young, extremely hot stars like these are emitting intense ultraviolet light which strips the surrounding gas of its electrons and causes it to emit the faint glow seen in this image. Given the right conditions, this material could one day collapse in on itself and provide the Milky Way with yet another brood of stars — a star formation process that may continue indefinitely.

This mammoth 30 577 x 20 108 pixel image was captured using the OmegaCAM camera, which is attached to the VLT Survey Telescope (VST) at ESO’s Paranal Observatory in Chile.

A spectacular image from ESO’s Wide Field Imager at the La Silla Observatory in Chile shows the brilliant and unusual star WR 22 and its colourful surroundings. WR 22 is a very hot and bright star that is shedding its atmosphere into space at a rate many millions of times faster than the Sun. It lies in the outer part of the dramatic Carina Nebula from which it formed.

Very massive stars live fast and die young. Some of these stellar beacons have such intense radiation passing through their thick atmospheres late in their lives that they shed material into space many millions of times more quickly than relatively sedate stars such as the Sun. These rare, very hot and massive objects are known as Wolf–Rayet stars, after the two French astronomers who first identified them in the mid-nineteenth century, and one of the most massive ones yet measured is known as WR 22. It appears at the centre of this picture, which was created from images taken through red, green and blue filters with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. WR 22 is a member of a double star system and has been measured to have a mass at least 70 times that of the Sun.

WR 22 lies in the southern constellation of Carina, the keel of Jason’s ship Argo in Greek mythology. Although the star lies over 5000 light-years from the Earth it is so bright that it can just be faintly seen with the unaided eye under good conditions. WR 22 is one of many exceptionally brilliant stars associated with the beautiful Carina Nebula (also known as NGC 3372) and the outer part of this huge region of star formation in the southern Milky Way forms the colourful backdrop to this image.

The subtle colours of the rich background tapestry are a result of the interactions between the intense ultraviolet radiation coming from hot massive stars, including WR 22, and the vast gas clouds, mostly hydrogen, from which they formed.